Low power sensing via resistive sensor matrix

ABSTRACT

Embodiments are disclosed that relate to input devices. In one embodiment, an input device comprises a sensor matrix having first and second pluralities of conductors, a plurality of first resistors, a voltage-applying mechanism configured to apply a selected voltage to each second conductor of the plurality of second conductors, a plurality of sensors, a scanning sensing circuit, and a wake-up sensing circuit. Each first resistor is connected in series between a first voltage and a conductor of the plurality of first conductors. Each sensor includes a switch in series with a matrix resistor, and each sensor is connected to one of the plurality of first conductors and one of the plurality of second conductors. The scanning sensing circuit is connected to each of the plurality of first conductors, and the wake-up sensing circuit is connected to each of the plurality of second conductors.

BACKGROUND

An input device, such as a touch sensor or a keyboard, may include asensor matrix having a switch for each sensor. In one example, akeyboard may include keys and a sensor matrix with a first set ofconductors arranged in rows and a second set of conductors arranged incolumns. Each key may include a switch connecting one row and one columnwhen the key is pressed. The pressed key may be identified by scanningthe column conductors and sensing the row conductors with a scanningsensing circuit.

SUMMARY

Various embodiments are disclosed herein that relate to sensor matricesand input devices. For example, one disclosed embodiment provides aninput device comprising a sensor matrix including a plurality of firstconductors, a plurality of second conductors, a plurality of firstresistors, and a voltage-applying mechanism configured to apply aselected voltage to each second conductor of the plurality of secondconductors. Each first resistor is connected in series between a firstvoltage and a first conductor corresponding to the first resistor. Thesensor matrix further comprises a plurality of sensors, a scanningsensing circuit, and a wake-up sensing circuit. Each sensor includes aswitch in series with a matrix resistor, wherein the sensor is connectedto a first conductor corresponding to the sensor and a second conductorcorresponding to the sensor. The scanning sensing circuit is operativelyconnected to each conductor of the plurality of first conductors, andthe wake-up sensing circuit is operatively connected to each conductorof the plurality of second conductors.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example embodiment of an input device including a sensormatrix.

FIG. 2 shows an example embodiment of a sensor matrix including awake-up sensing circuit and a scanning sensing circuit.

FIG. 3 shows another example embodiment of a sensor matrix including awake-up sensing circuit and a scanning sensing circuit.

FIG. 4 shows an example embodiment of a method of operating an inputdevice.

DETAILED DESCRIPTION

Various embodiments are disclosed herein that relate to the low-powersensing of a sensor matrix in an input device. An input device, such asa touch sensor (e.g. a resistive touch screen), a computer keyboard, amusical keyboard, or other such input device comprising a matrix ofinput coordinates may include a sensor switch at each coordinate that isconfigured to receive input. The sensors may be connected such that eachswitch is connected to a conductor from a set of first conductors and aconductor from a set of second conductors different from the set offirst conductors. Thus, when one sensor is active, the sensor may beidentified by knowing which conductors are connected by the closedswitch of the sensor.

When multiple sensors are active, a conventional sensor matrix may notbe able to correctly identify the correct active sensors. For example, akeyboard may include rows A and B, columns 1 and 2, and a key at anintersection of each row and column. Each key may be identified by itsassociated row and column, such that the keys may be labeled A1, A2, B1,and B2. When three of the four keys are pressed (e.g. active), theinactive key cannot be identified because rows A and B and columns 1 and2 are shorted together by any combination of three or four of the keysbeing active. This aspect of the conventional keyboard may be referredto as “ghosting” or “phantom keys.”

One past solution to this problem is to insert a diode in series witheach switch. By doing this, every combination of closed switches createsa unique set of current paths between rows and columns. Thus, anycombination of closed switches can be correctly determined. However, theadditional diodes may add significant cost. A further complication isthat many keyboards use flexible membranes, printed with conductivematerial, to create the switches and their connections. This technologydoes not easily allow for the addition of the required diodes.

To address this issue, a sensor matrix may utilize resistors rather thandiodes in series with each switch to allow any combination of closedswitches to be uniquely determined. Such a configuration is shown hereinwith reference to FIGS. 2-3, described below. Unlike the diode approach,the resistive matrix uses a current measurement, rather than a voltagemeasurement to determine switch state. However, a disadvantage of thistechnique is that the current measurement circuitry requires power tooperate, even when the keyboard is sitting idle, waiting for a key pressto Occur.

Thus, to reduce the power consumption of such circuitry, a usefultechnique is to enter a low-power sleep mode during periods ofinactivity. When using this technique, a mechanism provided fordetecting when activity resumes so that sleep mode may be exited. Oneoption would be to use a timer to wake periodically to scan the matrixto see if any activity is occurring. To achieve low power, the sleeptimes should be as long as possible. However, it is possible thatactivity could start and stop while sleeping. To catch this activity,the system should wake frequently. Thus, there is a fundamental tradeoffbetween power and responsiveness.

An alternative technique is to use the “wake-on-change” featureavailable on many microcontrollers. Using this, the system wakes fromsleep when the state of a pin changes. There is no need for periodicscanning, and if configured properly, closing any switch willimmediately trigger the transition out of sleep mode. This may allow forboth maximum sleep time (minimizing power) and optimal responsiveness.

Therefore, embodiments are disclosed herein that relate to enabling aresistive sensor matrix to wake up a microprocessor on a GPIO edgeinterrupt when a sensor matrix switch is activated. Prior to discussingthese embodiments, an example of a suitable use environment is firstdescribed. FIG. 1 illustrates a block diagram of an example embodimentof an input device 100. Non-limiting examples of input devices mayinclude keyboards, resistive touch sensitive devices, and other inputdevices comprising a resistive sensor matrix. Input device 100 mayinclude a touch interface 110. In one embodiment, touch interface 110may include a touch sensor 112, such as on a touch sensitive inputdevice. In another embodiment, touch interface 110 may include keys 114,such as on a keyboard input device. Touch interface 110 is connected toa sensor matrix 120, such as a keyboard or touch sensor.

A controller 130 may be configured to execute instructions to carry outmethods of scanning and sensing the conductors as well as otherfunctions of input device 100. The instructions may be encoded andstored in a computer readable medium, such as memory 140. Non-limitingexamples of controller 130 may include discrete logic gates, amicrocontroller, a microprocessor, logic in a programmable logic deviceor in an application specific integrated circuit (ASIC). Non-limitingexamples of memory 140 may include volatile and/or non-volatile memorysuch as Flash memory, read-only memory, random access memory, andremovable storage such as a digital versatile disc (DVD), Flash drive,CD-ROM, or other removable medium. Controller 130, memory 140, andcomponents of sensor matrix 120 may be integrated onto a common device,or provided separately.

Interface and communications components 150 may be used to communicateinformation between input device 100 and a computer or other device. Forexample, the identity of a pressed key may be transmitted to a computerthrough a Universal Serial Bus (USB) interface. Communications may bevia a wired or wireless interface, for example. Non-limiting examples ofinterface and communications components 150 may include interfaces toUSB, PS/2, RS-232, Ethernet, IEEE 802.11, or other suitable interfaces.Interface and communications components 150 may be integrated withcontroller 130, memory 140, and components of sensor matrix 120 in acommon device.

FIG. 2 illustrates a schematic of an example embodiment of sensor matrix120 configured to wake from a sleep state upon activation of a sensormatrix switch. Sensor matrix 120 comprises a plurality of firstconductors including conductor 210, a plurality of second conductorsincluding conductor 220, a plurality of first resistors includingresistor 212, and a plurality of second resistors including resistor222. While the plurality of first conductors extends horizontally andthe plurality of second conductors extends vertically in the schematicof FIG. 2, it will be appreciated that the orientation of the pluralityof conductors in the schematic is shown for the purpose of illustration,and is not intended to imply any particular physical arrangement offirst and second pluralities of conductors.

Each first resistor 212, which may be referred to herein as a“pull-down” resistor, is connected in series between a first voltage Vssand a first conductor corresponding to the first resistor. Each secondresistor 222, which may be referred to herein as a “pull-up” resistor,is connected in series between a second voltage Vdd and a secondconductor corresponding to the second resistor. The first resistors 212and second resistors 222 may have any suitable configuration. In oneembodiment, resistors 212 and 222 may be screen printed with a resistiveink, such as a carbon ink. In alternative embodiments, resistors 212 and222 may be surface mount, axial lead resistors, or any other suitabletype of resistor. In yet another embodiment, one or more of resistors212 and 222 may be integrated in an integrated circuit including amicrocontroller. For example, controller 130 may include programmableinput/output pins with programmable pull-up and/or pull-down resistors.The resistor values are chosen such that the pull-down resistors aresuitably smaller in resistance than the sensor resistors, which are inturn suitably smaller in resistance than the pull-up resistors.

Sensor matrix 120 further comprises a plurality of sensors 230, ascanning sensing circuit 240, and a wake-up sensing circuit 250.Different sensors are noted as A1-A3, B1-B3, and C1-C3 in FIG. 2, whereeach sensor represents a keyboard key, touch input location, or thelike. Each sensor 230 includes a switch 234 in series with a matrixresistor 232, and the sensor 230 is connected to a corresponding firstconductor 210 corresponding to the sensor and a second conductor 220corresponding to the sensor.

Scanning sensing circuit 240 is operatively connected to each firstconductor of the plurality of first conductors. In the depictedembodiment scanning sensing circuit 240 includes a plurality ofcomparators 260. Each comparator 260 includes an input connected to afirst conductor from the plurality of first conductors, an outputconnected to controller 130 (where the labels “ROW A,” “ROW B,” and “ROWC” are shown), and another input connected to a reference voltage 262.Likewise, each second conductor is connected to controller 130 where thelabels “COL 1,” “COL 2,” and “COL 3” are shown. In another embodiment,scanning sensing circuit 240 may include an analog to digital converter(ADC), such that the integrated ADC may be used for sampling an outputof each first conductor. In other embodiments, any other suitablescanning circuit may be used.

During scanning, controller 130 scans the sensor matrix by driving aselected second conductor of the plurality of second conductors highwhile leaving the others low. The pull-down resistors 212 are designedto sense the row current by slightly changing the voltage on the rowsproportional to the current. To first order, one can think of the rowvoltages as fixed at approximately ground. Since all of the columns arealso low, except the driven one, the only resistors that can havesubstantial voltage across them are the ones attached to the drivencolumn. Thus, the current in each pull-down resistor depends almostexclusively on the current provided by the corresponding sensor bridgingto the driven column. Comparators (260) are used to sense the smallvoltage rise that will occur if the sensor switch is closed. Thecontroller reads the output of each comparator to detect whether anysensor switches are closed. While the depicted embodiment is configuredto be read by driving the columns and scanning the rows, it will beunderstood that the depicted sensor matrix may be configured to be readyby driving the rows and scanning the columns.

During sleep mode, comparators 260 may be switched off This may allowthe current used by the input device to remain below a desiredthreshold, such as a USB suspend current specification (e.g. 500microamps), during sleep mode. This may help to meet the specificationsof standards such as USB, and/or also may allow for improved batterylife in battery-powered input devices.

However, when the comparators 260 are switched off, the controller 130is not able to scan the sensor matrix by looking at the output of thecomparators 260. Therefore, wake-up sensing circuit 250 may be used tomonitor the plurality of second conductors to determine when a sensormay have been activated. This may be performed as follows. During sleepmode, the controller 130 configures all of the columns, which are drivenas outputs during normal input device wake mode operation, to be digitalinputs. The controller 130 then powers down the comparators 260 (orother scanning sensing circuitry) to enter sleep mode. If no sensorswitches 232 are closed, then all of the second conductors 220 arepulled high by the second resistors 222. Controller 130 is configured towake up on any falling edge voltage on any of second conductors 220, andthen goes to sleep. Because comparator power is disconnected on the highside leaving only a connection to ground, the comparator 260 will notdrive the corresponding row to any voltage other than ground,independent of the design of the particular comparator used.

As long as a user does not actuate any sensor, the pull-up resistors(second resistors 222) hold the second conductors 220 high. Thecontroller 130 will therefore remain in sleep. On the other hand, when auser actuates a sensor (e.g. by pressing a keyboard key or touching aresistive touch sensor), a voltage divider is formed. For example, if auser activates the sensor at position A1, resister R4 of the pluralityof second resistors is pulling up, while the series resistors R1 (of theplurality of first resistors) and RA1 (i.e. the matrix resistor atposition A1) are pulling down. Use of a sufficiently large resistor forresistor R4 of the plurality of second resistors allows the resultingvoltage of the second conductor 222 to be detected as a logic low by thecontroller 130. Thus, the activation of the sensor at position A1 isdetected as a falling edge by controller 130, which causes thecontroller to enter the wake mode and power up the comparators 260 (orother scanning circuitry). Then, controller 130 scans the sensor matrixto determine which sensor is activated. In this manner, each switch isactuatable to form a voltage divider comprising one second resistor ofthe plurality of second resistors, the matrix resistor that is in serieswith the switch, and one first resistor of the plurality of firstresistors. This allows the wake-up sensing circuit to be triggered towake up the controller by detecting a voltage edge on any conductor ofthe plurality of second conductors.

The comparators 260 may be switched off in any suitable manner. Forexample, the Vdd terminal of the comparators 260 may be connected to aGPIO pin of controller 130 (which is driven high to turn the comparators260 on, or driven low to turn the comparators 260 off), by using adiscrete power transistor or other switch, or in any other suitablemanner.

Likewise, each of the resistors may have any suitable values. Forexample, in one specific example embodiment, resistor R1 has a value ofapproximately 1 kohm, resistor RA1 has a value of approximately 20 kohm,and resistor R4 has a value of approximately 1000 kohm, the voltagedivider produces an output of approximately (21 kohm/1021kohm)=approximately 0.02 times Vdd. It will be understood that thesespecific resistor values are presented for the purpose of example andare not intended to be limiting in any manner, and that the resistorsmay have any other suitable values. Suitable values for second resistors222 may include, for example, values that are sufficiently differentfrom the values of the matrix resistors to produce a voltage less thanthat recognized by the controller 130 to correspond to a low logiclevel. In some embodiments, the matrix resistors 232 may have valuesthat are significantly larger than the first resistors 212 (e.g. on adifferent order of magnitude). In other embodiments, the matrixresistors 232 may have values that are close to or even equal to thefirst resistors 212, as long as the sum of the matrix resistor 232 andfirst resistor 212 along any conductive pathway formed via a switchactuation is sufficiently small compared to the value of the secondresistor 222 along that conductive pathway for the wake-up sensingcircuit to operate as discussed above. Because current is lost throughany additional closed switches along a same first conductor 210, athreshold value of the first resistor 212 may be selected based upon aworst-case scenario of all switches along that first conductor 210 beingclosed simultaneously.

Likewise, suitable resistor values also may in some embodiments beselected based upon noise considerations. Due to the relatively highresistances of each second resistor 222 compared to each matrix resistor232, noise currents may produce a false low level on one of secondconductors 220. Thus, it may be possible that controller 130 may wake upupon observing spurious falling edges, electrostatic discharge events,radiated electromagnetic compatibility effects, and/or other similareffects. However, because controller 130 merely scans the sensor matrixwith the comparators 260 powered upon waking up, no false keystrokeswill be detected. Thus, such noise may cause only a slightly increasedcurrent due to the comparators being powered up. It will be understoodthat, where the matrix resistors are formed via printing with silver orcarbon ink or the like, resistances of the matrix resistors and/or thesecond resistors may be determined by the properties of the ink, andthat decreasing the resistance of the matrix resistors by printingthicker or fatter traces may increase the cost of the sensor matrix dueto the greater volume of ink used.

The embodiment of FIG. 2 may allow a significant reduction in powerconsumption compared to sensor matrices in which comparators 260 areleft powered up to detect sensor activation while controller 130 isasleep. For example, the power consumption of the embodiment of FIG. 2during sleep is substantially equal to the power consumption of aconventional keyboard during sleep. Further, it will further beunderstood that the wake-up sensing circuitry may perform correctly nomatter how the scanning circuitry (comparators or other) behaves whenpowered off. For example, when powered down, comparators 260 may sinkmore power to ground. This may help to increase the resistance pullingdown and decrease the voltage relative to when the comparators 260 arepowered on, thereby improving the noise margin and enhancing logic low.

It will be understood that the use of the first resistor 212, secondresistor 222, and matrix resistor 234 may be applied to any suitablecircuit used for scanning a sensor matrix, including, but not limitedto, circuits that utilize op-amp transimpedance amplifiers, discretetransistor amplifiers, a microcontroller's ADC, and/or any othersuitable scanning circuitry. In some embodiments, the plurality ofsecond resistors 222 may be omitted. In such embodiments, the controller130 may be configured to output logic high on each second conductor 220,and then to convert the GPIO pins connected to second conductors 220 tobe inputs. In this case, the stray capacitance of the GPIO pin andassociated circuitry may hold the corresponding second conductor 220high until a sensor activation pulls the second conductor 220 low. Itwill be understood that any suitable voltage-applying mechanism may beused to apply a logic high voltage to each second conductor of theplurality of second conductors, including but not limited to secondresistors 222 and controller 130.

FIG. 3 illustrates an example embodiment of a sensor matrix 300comprising a wake-up sensing circuit in which controller 130 is utilizedto set and maintain a voltage of each second conductor via GPIO pins andassociated stray capacitance, and/or via external capacitors, whereinsuch capacitance is illustrated schematically via capacitors 310. Inthis embodiment, when entering sleep mode, a voltage, such as V_(DD),may be applied to each of the plurality of second conductors until theplurality of capacitors is pre-charged to V_(DD) or near V_(DD). If nosensors are active, each of the capacitors 310 may stay charged nearV_(DD). Alternatively, each of the capacitors 310 may have a parasiticresistance that slowly bleeds charge from each of the capacitors. Thus,controller 130 (which is connected to sensor matrix 300 at the labels“COL 1,” COL 2,” and COL 3,” and at “ROW A,” ROW B,”, and ROW C”) maywake periodically to refresh the charge on each capacitor 310, and thenpower-down to re-enter sleep mode. If a sensor is active, its associatedcapacitor 310 may be discharged through the resistor of the sensor andthe resistor connected between the associated conductor of the pluralityof first conductors and the voltage rail, such as V_(SS). For example,when sensor matrix 300 is in sleep mode, each capacitor 310 may becharged to V_(DD). If sensor 320 is activated (e.g. switch 332 isclosed), capacitor 310 may be discharged through resistors 330 and 340.Discharging of capacitor 310 may generate a falling edge on conductor350 which may be detected by controller 130 so that controller 130 mayenter wake mode. Utilizing either of the embodiments of FIGS. 2-3,compared to waking from a timer to do periodic scanning, waking uponoccurrence of activity prevents such activity from being missed, therebyallowing for long sleep times.

FIG. 4 illustrates an example embodiment of a method 400 for detectingan active sensor of an input device, such as input device 100. It isunderstood that the processes shown in FIG. 4 are representativepresented for the purpose of illustration, and not intended to belimiting. For example, in various embodiments the illustrated processesmay be performed in a different order than that shown. Further, invarious embodiments, one or more of the illustrated processes may beomitted, and/or other processes not shown may be added.

At 410, a first voltage, such as V_(SS), may be applied to eachconductor of the plurality of first conductors. In one embodiment, thevoltage may be applied through a pull-down resistor, such as resistor212.

At 420, a second voltage, such as V_(DD), may be applied to eachconductor of the plurality of second conductors. In one embodiment, thevoltage may be applied through a pull-up resistor, such as resistor 222.In another embodiment, the voltage may be applied by a chargedcapacitor, such as capacitor 310 charged by controller 130, or in anyother suitable manner.

At 430, controller 130 is operated in a sleep mode. Other components mayalso be placed in a reduced power mode, such as scanning sensing circuit240. In this manner, the supply current of input device 100 may bereduced during some conditions.

At 440, a voltage of each conductor of the plurality of secondconductors may be sensed. In one embodiment, the voltage may be sensedby edge detection logic of an interrupt controller. In anotherembodiment, the voltage may be sensed by a channel of an ADC, or in anyother suitable manner.

At 450, a user actuation of a switch is received, in which a firstselected conductor from the plurality of first conductors is connectedto a second selected conductor from the plurality of second conductorsvia the closing of a switch (e.g. by a user depressing a key or pressingon a touch screen). Thus, conductor 220 may be connected to conductor210 through resistor 232.

At 460, an edge of the voltage of the second selected conductor from theplurality of second conductors is detected. In one embodiment, a fallingedge may be detected on a conductor, such as conductor 220. The fallingedge may, for example, be defined as a transition from V_(DD) to V_(SS),as a transition from V_(IH) to V_(IL), or in any other suitable manner.It will be understood that, in other embodiments, a rising edge may bedetected.

At 470, the controller may enter and operate in a wake mode when theedge of the voltage of the second selected conductor from the pluralityof second conductors is detected. Additional components of input device100 may be operated in a wake mode when the edge of the voltage of thesecond selected conductor from the plurality of second conductors isdetected. For example, current may be supplied to scanning sensingcircuit 240 during the wake mode.

Upon entering wake mode, at 480, a sensor matrix scan may be performedto detect a location of a user input, such as the location of a selectedkey that is pressed by a user. Next, at 490, it is determined if thescanning is still active. For example, in some embodiments, the scanningmode may be active until a predetermined amount of time passes withoutdetecting a switch actuation. If the scanning is still active, method400 returns to 480 to conduct another scan. On the other hand, ifscanning is no longer active, then method 400 returns to 410 to againprepare for and enter sleep mode.

In this manner, an input device may be operated in a manner configuredto lessen power consumption yet wake to detect user inputs. The inputdevice may use less supply current during sleep mode which may extendbattery life and/or comply with a USB maximum standby supply currentstandard. A transition from sleeping to waking may be triggered by anactive sensor which may further reduce power consumption compared to aninput device that periodically wakes up. In addition, waking on anactive sensor may reduce or eliminate missed key presses compared towaking periodically, since a key may be pressed and released during aperiodic sleep interval. Further, it will be understood that thedisclosed sensing and wake-up circuitry may be constructed usingoff-the-shelf components and microcontrollers of the type intended foruse in conventional input devices.

It is to be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific methods describedherein may represent one or more of any number of processing strategies.As such, various acts illustrated may be performed in the sequenceillustrated, in other sequences, in parallel, or in some cases omitted.Likewise, the order of the above-described processes may be changed.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

1. An input device comprising a sensor matrix, the sensor matrixcomprising: a plurality of first conductors; a plurality of firstresistors, each first resistor being connected in series between a firstvoltage and a first conductor corresponding to the first resistor; aplurality of second conductors; a voltage-applying mechanism configuredto apply a selected voltage to each second conductor of the plurality ofsecond conductors; a plurality of sensors, each sensor including aswitch in series with a matrix resistor, each sensor connected to afirst conductor corresponding to the sensor and a second conductorcorresponding to the sensor; a scanning sensing circuit operativelyconnected to each first conductor of the plurality of first conductors;a wake-up sensing circuit operatively connected to each second conductorof the plurality of second conductors.
 2. The input device of claim 1,wherein the voltage-applying mechanism comprises a plurality of secondresistors, each second resistor being connected in series between asecond voltage and a second conductor corresponding to the secondresistor.
 3. The input device of claim 2, wherein a resistance of eachsecond resistor is lower than a resistance of each matrix resistor. 4.The input device of claim 2, wherein each switch is actuatable to form avoltage divider comprising one second resistor of the plurality ofsecond resistors, the matrix resistor that is in series with the switch,and one first resistor of the plurality of first resistors, and whereinthe wake-up sensing circuit is configured to detect a voltage of eachconductor of the plurality of second conductors.
 5. The input device ofclaim 1, wherein the wake-up sensing circuit is configured to detect avoltage of each conductor of the plurality of second conductors.
 6. Theinput device of claim 1, wherein the voltage-applying mechanismcomprises a controller configured to apply a voltage to each secondconductor and also comprises a capacitor, and wherein the controller isconfigured to receive an input of one or more of a rising edge and afalling edge at each second conductor after applying the voltage to eachsecond conductor.
 7. A method for detecting an active sensor on an inputdevice via a controller, the method comprising: applying a first voltageto each conductor of a plurality of first conductors; applying a secondvoltage to each conductor of a second plurality of conductors when thecontroller is in the sleep mode; entering the controller in a sleepmode; sensing a voltage of each conductor of the plurality of secondconductors while in the sleep mode; receiving a user actuation of aswitch in series with a matrix resistor, the switch and the matrixresistor connected in series between a first selected conductor from theplurality of first conductors and a second selected conductor from theplurality of second conductors; detecting via the controller an edge ofthe voltage of the second selected conductor from the plurality ofsecond conductors; and entering the controller into a wake mode when theedge of the voltage of the second selected conductor from the pluralityof second conductors is detected.
 8. The method of claim 7, furthercomprising: upon operating the controller in the wake mode, scanningeach conductor from the plurality of second conductors, wherein scanningincludes applying the second voltage to a selected conductor from theplurality of second conductors and applying the first voltage to thenon-selected conductors of the plurality of second conductors; andsensing a current of each conductor of the plurality of firstconductors.
 9. The method of claim 7, wherein applying the secondvoltage to each conductor of the plurality of second conductors includespre-charging each conductor of the plurality of second conductors byapplying the second voltage.
 10. The method of claim 7, wherein thefirst voltage is applied to each conductor of the plurality of firstconductors through a first resistor in series with the first voltage,the second voltage is applied to each conductor of the plurality ofsecond conductors through a second resistor in series with the secondvoltage, and a resistance of the second resistor is greater than aresistance of the first resistor.
 11. The method of claim 7, wherein thesecond voltage is applied to each conductor of the plurality of secondconductors via an input/output pin of the controller prior to operatingthe controller in sleep mode, and further comprising, prior to operatingin sleep mode, converting the pin of the controller from an output pinto an input pin after applying the second voltage to each conductor ofthe plurality of second conductors.
 12. The method of claim 11, furthercomprising periodically waking the controller from sleep mode to refreshthe charge on each conductor of the plurality of second conductors andthen re-entering into sleep mode.
 13. The method of claim 7, furthercomprising: supplying current to a scanning sensing circuit during thewake mode; and disconnecting current to the scanning sensing circuitduring the sleep mode.
 14. A system for detecting a key pressed on akeyboard, comprising: a plurality of first conductors and a plurality offirst resistors, each conductor of the plurality of first conductorsconnected by a corresponding resistor of the plurality of firstresistors to a first voltage; a plurality of second conductors and aplurality of second resistors, each conductor of the plurality of secondconductors connected by a corresponding resistor of the plurality ofsecond resistors to a second voltage; a plurality of keys, each keyincluding a switch in series with a matrix resistor, each key connectedto a first conductor corresponding to the switch and a second conductorcorresponding to the switch; a scanning sensing circuit including aplurality of inputs connected to the plurality of first conductors; awake-up sensing circuit including a plurality of inputs connected to theplurality of second conductors; a controller operatively connected tothe scanning sensing circuit and the wake-up sensing circuit; and acomputer readable medium containing instructions encoded to execute onthe controller, the instructions configured to: put the controller in asleep mode; detect an edge of the voltage of each conductor of theplurality of second conductors; put the controller in a wake mode whenthe edge of the voltage of a conductor of the plurality of secondconductors is detected; and detect a selected key that is pressed. 15.The system of claim 14, wherein the plurality of second conductors areconnected to input/output pins of the controller.
 16. The system ofclaim 14, wherein a resistance of each resistor of the plurality ofsecond resistors is greater than a resistance of each resistor of theplurality of first resistors.
 17. The system of claim 14, wherein one ormore resistors of the plurality of first resistors and the plurality ofsecond resistors are integrated into one or more input/output pins ofthe controller.
 18. The system of claim 14, wherein the wake-up sensingcircuit is integrated into the controller.
 19. The system of claim 14,wherein the scanning sensing circuit includes a plurality ofcomparators, each comparator including a first input connected to onefirst conductor of the plurality of first conductors and a second inputconnected to a reference voltage.
 20. The system of claim 14, whereinpower for the scanning sensing circuit is controlled by an output pin ofthe controller and the computer readable medium further includesinstructions configured to power down the scanning sensing circuit whenthe system enters the sleep mode and to power up the scanning sensingcircuit when the system enters the wake mode.